Establishing And Application Of “Signal-on” Fluorescence Sensors Based On Graphene Quantum Dots

With the development of optical fiber technology, the optochemical sensors sensor has become one of the leading research topics. Fluorescence detection technology has the advantages of convenient, fast, high sensitivity, good selectivity, and can realize remote monitoring and timeliness, and has been widely used in various fields.Especially, the special function of molecular switch type fluorescent sensor has a unique attraction. Signal-on type fluorescent sensor has the advantages of small interference,high selectivity, fast response, good recovery, with a good application prospects.In this paper, we design and synthesize three kinds of "Signal-on" type fluorescent sensors for GSH and PPi detection and try to apply to cell imaging, which obtain satisfactory results. Provides a new detection method for clinical, help to achieve the diagnosis of disease. The full text is divided into three parts, as follows:Chapter 1 Signal-on fluorescent sensor based on GQDs-MnO₂ composites for glutathioneIn this part, a signal-on fluorescence sensor based on GQDs-MnO₂ composites was designed fordetection of glutathione?GSH?. The fluorescence of GQDs was quenched by MnO₂ in GQDs-MnO₂ composites caused by the fluorescence resonance energy transfer?FRET? in the internal. The fluorescence of GQDs was restored when GSH was introduced because GSH reduced the MnO₂ nanosheets into dissoluble Mn2+and released GQDs from the surface of MnO₂. Under optimized condition, the concentration of GSH can be accurately detected with high sensitivity and specificity in Tris-HCl buffer and simulated serum. The proposed sensing strategy successfully measured GSH in the range of 1-1000 ?M with a detection limit of 4.467 ×10-7M. In addition, the Reduced Glutatione Injection and Reduced Glutatione Tablets can be detected accurately using the propsed method. GQDs-MnO₂ composites are thus a promising GSH fluorescence sensor in complex systems and in the quality control in pharmaceutical industry.Chapter 2 Signal-on fluorescent sensor based on N-S/GQDs for cell imageIn this chapter, the fluorescence intensity of N-S/GQDs was quenched by MnO₂ in N-S/GQDs-MnO₂ composites caused by the fluorescence resonance energy transfer inthe internal. The fluorescence of N-S/GQDs was restored when GSH was introduced because GSH reduced the MnO₂ nanosheets into Mn2+ and released N-S/GQDs. Under the optimized experimental condition,the degree of recovery was positively correlated with the concentration of GSH in the range of 5-1200 ?M. The use of N-S/GQDs has good biocompatibility and high quantum yield advantages to cell imaging, achieved satisfactory results.Chapter 3 Switch-on fluorescent strategy based on N and S co-doped grapheme quantum dots?N-S/GQDs?for determination and application Fe³⁺ and PPiThis work reports a facile and effective approach for preparing graphene quantum dots co-doped with nitrogen and sulfur?N-S/GQDs?. The proposed method comprised pyrolysis of citric acid with glutathione and dialysis treatment. The fabricated NS/GQDs exhibited blue luminescence and a high fluorescence quantum yield of 36.3%.N-S/GQDs can be sensitively quenched by Fe³⁺, which was absorbed on the edge of NS/GQDs through the coordination interaction between Fe³⁺ and N, S elements. The degree of quenching is positively correlated with the concentration of Fe³⁺, which can be used for the detection of Fe³⁺.The subsequent introduction of pyrophosphate ion?PPi?, the stronger coordination reactivity between Fe³⁺and PPi induced changes in fluorescence, resulted in the recovery of the fluorescence of N-S/GQDs. PPi concentration was facilely quantified through the recovered amplitudes of the fluorescence intensities of N-S/GQDs. Under the optimized experimental condition,increased fluorescence intensity showed a linear relationship to PPi concentration?1-1000 ?M? with a detection limit of 8.13 × 10-7M. And can be used with the cell imaging.Additionally, the proposed method featured sensitive, selectivity and accuracy for the detection of PPi in synovial fluid, suggesting the potential application for simple and accurate clinical diagnosis of arthritic diseases.